Lower back pain is a common condition amongst the adult population and represents the most common cause of loss of work productivity. The aetiology of mechanical lower back pain includes a variety of conditions: 70% from lumbar strain or sprain; 10% from degenerative changes to discs and facets; 4% from herniated discs; 4% from osteoporotic compression fractures; 3% from spinal stenosis; and 1% from other causes (infection, ankylosing, spondylitis, neoplasms, etc.). When non-operative modalities fail, treatment may then require fusion for varied indications that include degenerative disc disease, spondylosis, age-related degeneration of the spine, infection, and primary or metastatic neoplasms. An estimated 350,000 spinal fusion procedures were performed in the US in 2004 at an estimated cost of 1.5-2 billion dollars. Nevertheless, even with new advancement in surgical treatment options, lower back pain still remains a formidable challenge to physicians in the United States. Therefore, the surgeon's task remains to develop and utilize innovative and effective ways of fusing a diseased spine while meeting the goals of surgical spine fusion, including restoration of alignment, halting of neurological progression, and amelioration of pain.
The conventional ventral mini-open retroperitoneal approach to the lower lumbar spine requires an initial incision usually less than 4 cm in length and is normally employed for ventral L4-5 and L5-S1 fusion. This procedure involves dissection through the skin, soft tissue, and the rectus abdominus muscle for access into the retroperitoneal space to expose the ventral lumbar spine. A number of anatomic structures may be injured during this dissection: the ureter; the common iliac arteries and veins and the median sacral vessels. Also, damage to the presacral plexus may result in premature ejaculation in males.
A conventional ventrolateral transpsoas approach has been developed for instrumentation of L1 through L4. With the patient positioned in a 90° lateral decubitus position, the spine is accessed laterally through the psoas muscle. Through this ventrolateral approach, morbidity from dural exposure, excessive nerve root retraction, epidural bleeding, and excessive scarring may occur. Furthermore, injury to the femoral or genito-femoral nerves may occur.
A conventional dorsal approach to the lumbar spine places the patient in a prone position and, through a midline incision over the level of interest, dissects and laterally retracts the dorsal paraspinal muscles. Apart from a significant risk of blood loss, the dural sac and the posterior rami, which lie between the transverse processes lateral to the pars interarticularis and the facet joint capsules, may be injured. Peri-operative pain and post-operative scarring are typically encountered following the dorsal approach.
Spinal fusion may be performed without or without a concomitant diskectomy, and the spine may or may not be instrumented. A particular technique used to effect spinal fusion relies both on the pathology in question and the expertise of the surgeon performing the procedure. The conventional gold standard for lumbar segmental spinal fixation is a ventral interbody graft with dorsal pedicle screws. Other conventional forms of fixation include ventral plates/rods with screws and dorsal transfacet fixation.
The vast majority of the approach-related morbidity associated with open instrumented lumbar fusion procedures is caused by extensive soft tissue muscle dissection and prolonged retraction of the soft tissues and muscle. Limited retraction and exposure has been related to improved clinical outcomes with less post-operative pain. Therefore, procedures of shorter duration involving minimal dissection and retraction are desirable.
Minimally invasive approaches to lumbar spine fixation may advantageously produce decreased morbidity, limited postoperative in-patient stay, decreased cost, and the potential to improve long-term outcomes. Improved forms of instrumentation have been developed to take advantage of various access corridors to the spine, such as percutaneous introduction of pedicle screws and rods. Development of minimally invasive ventral access corridors to the lumbar spine has lagged behind dorsal access. Expandable tube retractors to allow direct visualization have been developed to assist surgeons. Navigation systems also may serve as aids for the accurate placement of pedicle screws.
Further advances in minimally invasive lumbar fixation may involve the development of a segmental lumbar fusion technique that, when used alone, eliminates the need for dorsal incisions. This technique is only available for the L5-S1 spine segment.
Thus, minimally invasive techniques (to manage pathologic conditions in various surgical disciplines) may be successfully and reliably performed. Although the treatment of lumbar disc diseases via minimally invasive approaches is rapidly gaining acceptance, minimally invasive lumbar fusion procedures have only recently been developed and implemented. For example, a conventional axial lumbar interbody fusion/fixation uses a percutaneous pre-sacral approach for safely and effectively fusing the L5-S1 vertebral segment. There is therefore a need in the art for an improved spinal fixation apparatus and method that utilizes a minimally invasive approach with the inherent advantage of reduction in approach-related morbidity associated with conventional lumbar fusion.